AIX has a limit for cronjobs concurrently being run

Sounds reasonable in a way. But it's rather bad, if you are not aware of it, and your corporate OS Monitoring Services do not remind you of critical entries in the resp. cron log file. They may say something like:

there is crontab entry, that did not get executed, because we exceeded the maximum number of … – maybe you want to fix something here

I suppose, similar limits exist in every UNIX flavour.